1. Field of the Invention
The present invention relates, in general, to a rotor of an ultra high speed induction motor, in which a conductive bar is coupled to a slot of the rotor, and a method of manufacturing the same.
2. Description of the Related Art
Generally, induction motors are apparatuses that receive electric energy and convert it into a rotational motion, and include a stator, around which windings are distributed, and a cylindrical rotor which is inserted into the stator to cause an induced current by a magnetic field that is induced by alternating current flowing through the stator windings.
FIG. 1 is a perspective view showing a rotor of a conventional induction motor.
The rotor of the conventional induction motor includes a cylindrical stacked body 10 which consists of a plurality of loop type electric steel sheets that are stacked to form a cylinder, with slots (not shown) formed at regular intervals around circumferences of the sheets, a conductive bar 20 made of a conductive material (copper, aluminum, copper alloy, or the like) and inserted into the respective slots, and an end ring 30 which is coupled to upper and lower portions of the stacked body 10 such that it is combined with the conductive bars 20.
The conductive bar 20 has the length larger than the cylindrical stacked body 10, and is welded to a plurality of through-holes 32 of the upper and lower end rings 30 by means of brazing, soldering, or Ar-type welding, with the opposite ends thereof inserted through the through-holes of the upper and lower end rings.
In manufacture of the rotor, as shown in the figure, the lower end ring 30, the cylindrical stacked body 10, and the upper end ring 30 are sequentially arranged on a jig, and a fastening cover 110 is placed thereon and tightly fastened by a nut 120.
Then, the conductive bars 20 are inserted through the through-holes 32 of the end rings 30 and the slots of the cylindrical stacked body 10, and are welded to the end. rings by performing welding on a gap g between themselves and the through-holes 32 using the above-mentioned welding method. The gap g is created because the diameter of the slot and through-hole 32 is made larger than the diameter of the conductive bar 20 in order to facilitate the insertion of the conductive bar 20 into the slot and the through-hole 32.
While the rotor having the above-mentioned construction has mainly been applied to a high speed electric motor, with a tendency to demand an ultra high speed electric motor in the industrial fields, problems should be solved in connection with materials, strength, or deformation, for example, of the rotor for realizing the ultra high speed revolution.
This is because the rotor is subjected to deformation or defectiveness in joint parts due to a centrifugal force occurring upon ultra high speed revolution of the rotor, thereby causing a weakened balancing feature and reduced lifetime.
Particularly, since the conductive bars are only welded and bonded to the end rings, but are simply inserted into the cylindrical stacked body while maintain the gap therewith, upon high speed revolution, the above-mentioned problems may be intensified.